#include<iostream>
#include<cstdio>
#include<cmath>

using namespace std;

int main()
{
    double x1, x2, y1, y2, end, mid;
    cin >> x1 >> y1 >> x2 >> y2;
    mid = pow((x2 - x1), 2) + pow((y2 - y1), 2);
    end = sqrt(mid);
    printf("%.4lf", end);
    return 0;
}